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Dec 17, 2023

Slow Lane, Goodbye? Here's A Big Bore Kit For Your Honda CT125

Photo: Honda Yesterday, rtwPaul gave us a long list of survival tips, for

Photo: Honda

Yesterday, rtwPaul gave us a long list of survival tips, for traveling on a small, slow bike in our big, fast world. Today, we see another survival tip: Install a big-bore kit! Turns out there are quite a few options for Honda's CT125 mini-ADV.

That shouldn't be a surprise, since the CT125 engine is based on the Honda Grom, and people have been big-boring and otherwise hot-rodding the Grom for many years. We see some of these products available in English-speaking markets, but if you search a site like Webike, the potential is endless.

As a side note, this isn't just true of the CT125/Grom platform. Almost any small-cc machine from Japan has a lot of interesting performance parts available in its home market; if not there, you can always check in Europe as well.

But what if you don't want to deal with overseas shipping? Turns out that in the CT125's case, some of those performance parts are available in the US right now. Hard Racing Performance, based in Mooresville, North Carolina, now offers a 181cc Kitaco big bore kit for the CT125. It will set you back $1049 at current pricing (Hard Racing says regular MSRP is $1500), and for that money, you do not get a new fuel controller, which seems like it's something you might need. No doubt Hard Racing can recommend you an aftermarket component, though.

Here's the contents of the big bore kit:

Kit Contains:181cc FORGED PISTON– 181cc HARDPLATED cylinder– Piston, rings, pin, clips and gasket kit– Kitaco HighProfile Camshaft– Kitaco Forged Crank Shaft– Kitaco Forged H-Style Con-Rod– High Performance Cam Shaft & Head– New Reinforced Cam Chain– New HD Valve Springs– New HD Cylinder Studs– New Hi-flow Injector– NO Fuel Controller

Hard Racing recommends a 16-tooth front sprocket with this setup, and says repeatedly in the advert: "**Please NOTE: CT125 CANNOT Use the KITACO CRANK SHAFT**" … and we wonder what's up with that? It's probably because this kit appears to have originally been built for the Grom, and the CT has a few internal differences, despite its many similarities.

Here are the parts from Hard Racing. Looks like it was a Grom kit originally. Photo: Hard Racing

Like any aftermarket engine modification, your results will vary according to your care during the assembly and break-in process, and since you’re modifying something that was carefully designed to be reliable in a specific state of tune, you’re going to lose that reliability once you start messing with it (a lesson I’ve learned the hard way). Having said that, this looks like a fun project for a CT owner, and if you dare to buy one of these kits and try it, we want to hear how it worked out for you. Or if you’ve tried one of the other kits on the market (maybe you ordered one from Japan?), we’d like to hear about that as well.

See the big-bore kit here.